A. Field of the Invention
The present invention relates to a fastener for joining two plugs in coaxial alignment and in a plurality of relative orientations about the axis of alignment. Such fasteners are useful for joining models of molecular constituents to assemble models of complete molecular structures.
B. Description of the Prior Art
Models for illustrating molecular structures have been used by researchers and educators for over 100 years. Many different designs for molecular models have been described and a number of types of such models are commercially available. Molecular models presently in wide use are discussed in the following two articles:
"The Use of Models in Stereochemistry," Anne Walton, Progress in Stereochemistry, 4, 335-375(1968); and PA1 "A Survey of Atomic and Molecular Models," Arnold J. Gordon, J. Chem. Educ., 47, 30-32(1970).
Because of the virtually infinite number of molecular structures found in nature, it is impractical to market only models of complete molecular structures. Instead, sets are available which include models of a number of atoms, functional groups, or other molecular constituents. The user selects the appropriate molecular constituents from the set and connects them together to assemble a model of the complete molecular structure of interest.
The mechanism by which such models of molecular subunits are joined together has been a source of recurring problems in the prior art. Difficulties arise because molecules can be made up of a great number of atoms, and thus models of such molecules are often large, unwieldly structures which tend to distort easily from the correct configuration. In order to obtain the maximum benefit from a model of a molecule, it is desirable to be able to view the model from any orientation. For this reason, it is desirable to be able to handle the model, which requires that the model be capable of maintaining its structural integrity when held in any orientation. Thus connections between the subunits of a molecular model are preferably rigid and mechanically secure. On the other hand, it is desirable that the mechanism by which the subunits are interconnected permit rapid assembly and disassembly of the model.
A further difficulty concerns the angular relationships among the subunits making up a molecular model. Models of molecular constituents are typically connected along chemical bonds within a molecule. In nature, the orientation which a molecular constituent assumes relative to another molecular constituent bonded to it is not fixed, but in general varies from molecule to molecule and can even vary among different configurations of the same molecule. Thus the mechanism for joining two models of molecular constituents along a chemical bond should be capable of joining the models both rigidly and in a variety of different relative orientations about the axis of the bond.
A widely used set of molecular models are the "framework molecular models" described U.S. Pat. No. 3,333,349 to Brumlik. Framework molecular models include coupling elements which represent atomic valence clusters and consist of thin cylindrical arms meeting at a center point corresponding to the center of an atom. Coupling elements representing atoms are joined by sections of elastomeric tubing which represent bonds. The tubing sections are of a size to receive the cylindrical arms of the coupling elements and to retain them by friction. Because the frictional connection is of limited strength, the size of molecular models which can be assembled from framework molecular models is limited. The weight of large molecular models tends to cause the frictional couplings to slip, thereby distorting the molecular structure. For very large molecular models, such frictional couplings can actually pull apart under the weight of the model.
A second type of molecular models, referred to as the Kendrew skeletal models, provides a more secure coupling between molecular constituents. The Kendrew skeletal models are described in the article by Walton cited above at pages 364-365. The models consist of units made of rigid brass rod. To connect two units, the ends of two rods are inserted into a small metal barrel which has two screws passing through its sides. The screws are tightened until they lock into grooves at the ends of the rods, thereby connecting the rods rigidly. However, assembly of a large molecule from the Kendrew skeletal models is an extremely slow and tedious process since it involves the tightening of two screws for each unit to be joined. To construct a model representing a large biochemical molecule, it may be necessary to make hundreds of such connections.